Phase 3 study demonstrates benefits of the first influenza vaccine to combine three proven approaches to enhancing protection for older adults in a single vaccine.

MAIDENHEAD, United Kingdom, Sept. 10, 2026 /PRNewswire/ — CSL Seqirus, a business of CSL (ASX: CSL; USOTC: CSLLY), today announced publication of pivotal Phase 3 study results for its MF59^®-adjuvanted cell-based higher-dose quadrivalent influenza vaccine (aQIVc) in The Lancet Infectious Diseases, marking an important milestone in the evolution of influenza prevention for older adults.¹

The publication follows approval of the trivalent formulation of aQIVc by the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom earlier this year for adults aged 50 years and older.² The vaccine, marketed as AUJEMFLU^®, has also been approved by the European Commission for adults aged 50 years and above.

The peer-reviewed publication reports findings from a large-scale study of the first influenza vaccine to combine three proven approaches to enhancing protection in older adults: MF59^® adjuvant, cell-based manufacturing, and a higher dose formulation compared to standard influenza vaccines.^1,3

Each of these approaches has been used separately in influenza vaccines for many years and is supported by extensive clinical and real-world evidence. This publication provides the first large-scale evaluation of their combination within a single vaccine.^1,2

Influenza remains a significant public health challenge, causing substantial illness, hospitalisations and deaths each year despite widespread vaccination programmes.⁴ 

Older adults are particularly vulnerable because the immune system becomes less responsive with age, reducing its ability to mount a strong protective response following vaccination.⁵ 

aQIVc combines three proven approaches to enhancing vaccine protection in older adults, with each playing a distinct and complementary role. Cell-based manufacturing helps preserve a closer match to circulating influenza strains, MF59® adjuvant strengthens, broadens and lengthens the immune response and a higher dose formulation further optimises that response.^2,6,7,8

The Phase 3 randomised immunogenicity and safety study enrolled 7,699 adults aged 50 years and older across eight countries and compared aQIVc with two enhanced influenza vaccines. The study met its primary objectives and demonstrated:¹

• Superiority versus the adjuvanted egg-based influenza vaccine comparator across all four influenza strains and age groups assessed.
• Non-inferiority versus a recombinant influenza vaccine for three out of four strains in the 50+ age group and four out of four strains in those aged 65+.
• Immune responses that persisted throughout the influenza season.
• A well-tolerated safety profile. Most reactions were mild or moderate and resolved within three days.¹  

The publication also reported exploratory findings of enhanced neuraminidase antibody responses versus comparators. The role of neuraminidase antibodies is an emerging area of influenza research that may contribute to reduced disease severity and broader protection beyond traditional measures of vaccine response.⁹

The study authors concluded that the findings support further evaluation of the vaccine and provide evidence for National Immunisation Technical Advisory Groups considering enhanced influenza vaccination strategies for older adults.¹

Regulatory submissions for the trivalent formulation of aQIVc have been made in multiple markets, with introductions expected to occur through a phased approach aligned to local regulatory, policy and access pathways.

Gregg Sylvester, Chief Medical Officer and Head of Research & Development, CSL Seqirus, said:
“Publication in The Lancet Infectious Diseases is a significant milestone for CSL Seqirus and reflects decades of investment in influenza vaccine innovation.”

“These findings provide important new evidence for healthcare professionals, policy makers and immunisation advisory groups considering future influenza vaccination strategies for older adults.”

Professor Colin Russell, Chair of the European Scientific Working Group on Influenza (ESWI) and Professor of Applied Evolutionary Biology at Amsterdam University Medical Center, said:
“Influenza vaccine innovation has historically progressed through incremental advances in technology and manufacturing. What makes this study noteworthy is that it shows the potential benefit of bringing multiple proven approaches together in a single vaccine.”

“Given the continued burden of influenza-related illness, hospitalisation and death among older adults despite widespread vaccination, these findings represent an important contribution to ongoing efforts to improve protection in this vulnerable population.”

About the Phase 3 Study
The randomised, observer-blind Phase 3 immunogenicity study enrolled 7,699 adults aged 50 years and older across Canada, Denmark, Estonia, Germany, Pakistan, the Philippines, the United Kingdom and the United States. Participants received either the MF59-adjuvanted cell-derived higher dose quadrivalent vaccine, an MF59-adjuvanted egg-based quadrivalent influenza vaccine or a recombinant quadrivalent influenza vaccine. The study evaluated immunogenicity, safety and manufacturing consistency.

About aQIVc
aQIVc is an MF59-adjuvanted, cell-based higher-dose quadrivalent influenza vaccine developed for adults aged 50 years and older.  The trivalent formulation has been licensed for use in people aged 50 and above in the UK and by the European Medicines Agency where it is marketed as AUJEMFLU.^®

The vaccine combines three proven approaches designed to enhance protection in older adults:

• MF59 adjuvant technology
• Cell-based manufacturing
• A higher dose formulation versus standard dose influenza vaccines
• Each dose contains 45 micrograms of haemagglutinin per influenza strain and 19.5 mg of MF59 adjuvant²

About CSL Seqirus
CSL Seqirus is part of CSL (ASX: CSL). As one of the largest influenza vaccine providers in the world, CSL Seqirus is a major contributor to the prevention of influenza globally and a transcontinental partner in pandemic preparedness and response. With state-of-the-art production facilities in the US, the UK and Australia, CSL Seqirus utilises egg, cell and adjuvant technologies to offer a broad portfolio of differentiated influenza vaccines in more than 20 countries around the world. For more information about CSL Seqirus, visit www.CSL.com.

Intended Audience
This press release is issued by CSL Seqirus and is intended to provide information about our global business. Information relating to the approval status, product labels, recommendations and availability of CSL Seqirus products may vary from country to country. Please consult your local regulatory authority for information on approval status and local prescribing information.

Forward-Looking Statements
This press release may contain forward-looking statements, including statements regarding future results, performance, regulatory milestones, product availability or achievements. These statements involve known and unknown risks, uncertainties and other factors which may cause actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Given these uncertainties, you should not place undue reliance on forward-looking statements.

For more information, please contact:
MEDIA CONTACT 
Alex Kiefer
Alex.Kiefer@Seqirus.com
Director International & Pandemic Communications, CSL Seqirus 

GL-aTIVc-26-0011

References

¹ Essink BJ, Vermeulen W, Andrade C, Mazur M, de Rooij R, Heijnen E, et al. Immunogenicity and safety of an MF59-adjuvanted cell-derived higher-dose quadrivalent influenza vaccine (aQIVc) in adults aged 50 years or older: a phase 3 randomised controlled trial. Lancet Infect Dis. In press 2026. Volume 26. September 2026.  THELANCETID-D-26-00167R3.
² Aujemflu suspension for injection in pre-filled syringe: summary of product characteristics [Internet]. Maidenhead: Seqirus UK Limited; 4 June 2026 (PL 47991/0020). Available from: https://www.medicines.org.uk/emc/product/102343/smpc cited 2026 Aug 2.
³ Ashraf M, Boivin W, Nguyen-Van-Tam JS, Nolan T, Stein AN, Russell CA. Development of an adjuvanted, higher-dose, cell-based influenza vaccine: combining advanced technologies to improve vaccine effectiveness. Expert Rev Vaccines. 2026;25(1):2667732. doi:10.1080/14760584.2026.2667732.
⁴ World Health Organization. Influenza (seasonal): fact sheet [Internet]. Geneva: WHO; 28 February 2025. Available from: https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)  cited 2026 Aug 28.
⁵ Cadar AN, Martin DE, Bartley JM. Targeting the hallmarks of aging to improve influenza vaccine responses in older adults. Immun Ageing. 2023;20:23. doi:10.1186/s12979-023-00348-6.
⁶ Essink BJ, Vermeulen W, Andrade C, de Rooij R, Isakov L, Casula D, et al. A randomised phase 2 immunogenicity and safety study of a MF59-adjuvanted quadrivalent subunit inactivated cell-derived influenza vaccine (aQIVc) in adults aged 50 years and older. Vaccine. 2025;51:126791. doi:10.1016/j.vaccine.2025.126791.
⁷ de Looze F, Essink BJ, van Boxmeer J, Andrade C, de Rooij R, Casula D, et al. Immunogenicity and safety of higher-dose cell-based adjuvanted quadrivalent influenza vaccines: combined results of randomised, controlled dose-finding and dose-confirmation studies. Vaccine. 2026;79:128436. doi:10.1016/j.vaccine.2026.128436.
⁸ Ashraf M, Stein AN, Youhanna J, Rockman S, McMahon M, McGovern I, et al. The impact of egg adaptation and immune imprinting on influenza vaccine effectiveness. Vaccine. 2025;62:127393. doi:10.1016/j.vaccine.2025.127393.
⁹ Monto AS, Petrie JG, Cross RT, Johnson E, Liu M, Zhong W, et al. Antibody to influenza virus neuraminidase: an independent correlate of protection. J Infect Dis. 2015;212(8):1191-99. doi:10.1093/infdis/jiv195.

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